its really not hard. you just get a metal container that can withstand heat (like a 35 or 55 gal drum) fill it with wood and put the lid on (make sure there is an air hole closer to the top). light a large fire under the barrel and keep it going for a while. you are just trying to heat the wood up in a low to no oxygen environment so that all the volatile stuff gasses off and you are left with carbon

it takes a lot of wood though for what you get out of it but if you have a huge amount of wood its not to bad
-matt